In pneumatic antilock brake systems of wheeled vehicles, such as motor vehicles and rail vehicles, that is to say pneumatic brake systems fitted with an antilock system, a valve unit for modulating the pressure is arranged in each of the brake lines leading from a brake valve to the wheel brake cylinders. This valve unit has an inlet valve and an outlet valve. By the inlet valve, a brake pressure outlet can be either connected to a brake pressure inlet or shut off from the latter. The brake pressure outlet is connected to a brake line segment leading to at least one wheel brake cylinder, and a brake line segment coming from the brake valve is connected to the brake pressure inlet. By the outlet valve, the brake pressure outlet can either be connected to a vent outlet or shut off from the latter, said vent outlet usually leading to the environment via a muffler.
Owing to the large flow volumes to be switched and correspondingly large path cross sections to be opened and closed, the inlet valve and the outlet valve are often designed as pneumatically actuable diaphragm valves, which can be controlled by a respective pilot valve designed as a 3/2-way solenoid valve. A diaphragm valve has a flexible diaphragm substantially in the form of a circular disk, which is clamped at its edge in a valve housing. Arranged on the axial inner side of the diaphragm, where the flow channels connected to the compressed air inlets and compressed air outlets are arranged, are a central circular valve seat of a cylindrical inner flow channel and an annular outer flow channel arranged concentrically with the inner flow channel. Arranged on the axially opposite outer side of the diaphragm is a control chamber, which can be supplied by the associated pilot valve either with a high control pressure generally taken from the brake pressure inlet or with a low control pressure (ambient pressure) generally taken from the vent outlet.
When the control chamber is supplied with the high control pressure, the diaphragm is pressed against the valve seat, whereby the inner flow channel is shut off from the outer flow channel, this corresponding to the closed state of the relevant diaphragm valve. When the control chamber is supplied with the low control pressure, the diaphragm, which generally rests automatically on the valve seat by virtue of its shape, is raised from the valve seat by the brake pressure prevailing in the flow channels and is moved in the direction of the control chamber, whereby the inner flow channel is connected to the outer flow channel, this corresponding to the open state of the relevant diaphragm valve.
A valve unit of this kind has the operating functions of “pressure buildup”, “pressure maintenance” and “pressure reduction”. In the operating function of “pressure buildup” of the valve unit, the inlet valve is open and the outlet valve is closed, with the result that the brake pressure fed in at the brake pressure inlet via the brake valve is transmitted unchanged to the brake pressure outlet and to at least one wheel brake cylinder connected thereto. Since the operating function of “pressure buildup” corresponds to the state of rest of the valve unit, the pilot valve of the inlet valve connects the control chamber of the inlet valve to a control line carrying the low control pressure when the solenoid of said pilot valve is in the deenergized state. The pilot valve of the outlet valve likewise connects the control chamber of the outlet valve to a control line carrying the high control pressure when the solenoid of said pilot valve is in the deenergized state.
In the operating function of “pressure maintenance” of the valve unit, the inlet valve and the outlet valve are closed, with the result that the brake pressure applied to the brake pressure outlet and the at least one wheel brake cylinder connected thereto is then held constant. To set this operating function, only the pilot valve of the inlet valve is switched over by energizing its solenoid, thus supplying the control chamber of the inlet valve with the high control pressure. In the operating function of “pressure reduction” of the valve unit, the inlet valve is closed and the outlet valve is open, with the result that the brake pressure outlet and the at least one wheel brake cylinder connected thereto are then vented to the environment. To set this operating function, both pilot valves are switched over by energizing their solenoids, thus supplying the control chamber of the inlet valve with the high control pressure and the control chamber of the outlet valve with the low control pressure.
The operating functions of “pressure maintenance” and “pressure reduction” of the valve unit are antilock functions, by which braking-induced locking of the at least one associated wheel is supposed to be avoided. These operating functions are controlled by corresponding control of the pilot valves by a control unit of an antilock system, in which the signals from wheel speed sensors are evaluated to detect imminent or already existing locking of the braked wheels.
With regards to the geometrical arrangement of the compressed air inlets and compressed air outlets of the inlet and outlet valves designed as diaphragm valves and of the pilot valves designed as solenoid valves in a valve housing, different embodiments of valve units are known.
In DE 22 24 274 C3, there is a description of a valve unit in which, in the installed position, the brake pressure inlet is arranged horizontally and the brake pressure outlet and the vent outlet are arranged so as to be aligned vertically downward in the valve housing. The inlet valve is arranged in the valve housing adjacent to the brake pressure inlet with its actuation axis aligned vertically and its diaphragm aligned horizontally, whereas the outlet valve is arranged horizontally opposite in the valve housing with its actuation axis aligned horizontally and its diaphragm aligned vertically. The pilot valve of the inlet valve is arranged in the valve housing above the diaphragm of the inlet valve, with its actuation axis aligned horizontally, whereas the pilot valve of the outlet valve is arranged with its actuation axis aligned vertically, between the diaphragm of the outlet valve and a vertical outer wall of the valve housing.
DE 40 05 608 A1, on the other hand, discloses a valve unit in which, in the installed position, the brake pressure inlet and the brake pressure outlet are arranged axially opposite in horizontal alignment and the vent outlet is arranged in horizontal alignment above the brake pressure outlet in the valve housing. The inlet valve is arranged approximately centrally below the brake pressure inlet and the brake pressure outlet in the valve housing, with its actuation axis aligned vertically and its diaphragm aligned horizontally, whereas the outlet valve is arranged centrally above the vent outlet in the valve housing, with its actuation axis aligned vertically and its diaphragm aligned horizontally. The pilot valve of the inlet valve is arranged in the valve housing with its actuation axis aligned horizontally, below the diaphragm of the inlet valve, whereas the pilot valve of the outlet valve is arranged centrally above the diaphragm of the outlet valve in the valve housing, with its actuation axis aligned vertically.
In another valve unit in accordance with DE 40 08 095 A1, in the installed position the brake pressure inlet and the brake pressure outlet are arranged in a horizontal alignment in the valve housing, likewise substantially axially opposite one another, but the vent outlet is arranged approximately centrally and aligned vertically downward in the valve housing. The inlet valve is arranged in the valve housing substantially centrally above the brake pressure inlet and the brake pressure outlet, with its actuation axis aligned vertically and its diaphragm aligned horizontally, whereas the outlet valve is arranged in the valve housing below the brake pressure outlet, with its actuation axis aligned vertically and its diaphragm aligned horizontally. The pilot valve of the inlet valve and the pilot valve of the outlet valve are then arranged in the valve housing with their respective actuation axes aligned vertically and with opposite switching directions, below the brake pressure inlet and radially adjacent to one another.
DE 34 08 123 A1 describes two embodiments of valve units. A first embodiment of the valve unit in accordance with FIG. 1 of that document corresponds to a large extent to the valve unit described above with reference to DE 40 08 095 A1. In a second valve unit in accordance with FIG. 2 of that document, in an installed position the brake pressure inlet and the brake pressure outlet are arranged to a large extent axially opposite one another in horizontal alignment in the valve housing, but the brake pressure outlet is arranged lower than the brake pressure inlet in the valve housing. The vent outlet is arranged approximately centrally and aligned vertically downward in the valve housing. The inlet valve and the outlet valve are arranged approximately at the level of the brake pressure inlet and the brake pressure outlet, with their actuation axes aligned horizontally and their diaphragms aligned vertically, at right angles to the brake pressure inlet and the brake pressure outlet, at offset heights relative to one another and axially opposite one another. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged in the valve housing with their respective actuation axes aligned vertically and with opposite switching directions, below the respectively associated diaphragm valve.
In the installed position in another valve unit, known from DE 38 25 549 A1, the brake pressure inlet and the brake pressure outlet are arranged axially opposite one another in horizontal alignment in the valve housing, and the vent outlet is arranged above the brake pressure inlet in horizontal alignment in the valve housing. The inlet valve is arranged above the brake pressure inlet in the valve housing, with its actuation axis aligned horizontally and its diaphragm aligned vertically, whereas the outlet valve is arranged above the brake pressure outlet in the valve housing, coaxially with the inlet valve, with its actuation axis aligned horizontally and its diaphragm aligned vertically. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged radially adjacent to one another, largely centrally above the diaphragms of the inlet valve and of the outlet valve, in the valve housing, with their respective actuation axes aligned horizontally and with opposite switching directions.
By virtue of the arrangement of the compressed air inlets and compressed air outlets, of the inlet valves and outlet valves and of the pilot valves, a multi-part embodiment and expensive mechanical machining of the valve housing are required with the abovementioned valve units. Especially the respective arrangement of the diaphragms of the inlet valve and of the outlet valve in different diaphragm planes requires repeated re-clamping of the housing parts for mechanical machining of the valve seats and of the channel edges or chamber edges between which the diaphragms are clamped. To reduce the production outlay, there have therefore already been proposals for valve units in which the diaphragm valves are arranged with parallel actuation axes and arrangement of the diaphragms in a common diaphragm plane corresponding largely to a parting plane between two housing parts.
A valve unit of this kind is described in DE 25 17 571 A1, for example. In this known valve unit, an elongate valve housing is subdivided by a parting plane that is horizontal in the installed position into a housing bottom part and a housing top part. The brake pressure inlet and the vent outlet are arranged in the longitudinal direction in horizontal alignment and substantially axially opposite in the housing bottom part, and the brake pressure outlet is arranged to a large extent centrally and at right angles thereto in the housing bottom part, likewise in horizontal alignment. The diaphragm valves are arranged in series in the longitudinal direction in the housing bottom part, between the brake pressure inlet and the vent outlet, with parallel actuation axes and arrangement of the diaphragms in a common diaphragm plane largely corresponding to the parting plane, being clamped between the housing bottom part and the housing top part in the longitudinal direction of the valve housing. The pilot valve of the inlet valve and the pilot valve of the outlet valve are each arranged radially adjacent to one another, above the respectively associated diaphragm valve, in the housing top part, with their respective actuation axes aligned vertically and the same switching directions, with the result that the overall height of the housing top part and hence of the valve unit as a whole is relatively large.
In another valve unit of this kind, which is known from EP 0 498 584 B1, the valve housing is subdivided by a parting plane that is vertical in the installed position into an inlet housing and an outlet housing. The brake pressure inlet is arranged in horizontal alignment at the top of the inlet housing. The brake pressure outlet is arranged in horizontal alignment, to a large extent axially opposite the brake pressure inlet, in the outlet housing, whereas the vent outlet is arranged in vertically downward alignment in the outlet housing. The diaphragm valves are arranged in the outlet housing between the brake pressure outlet and the vent outlet with parallel actuation axes and arrangement of the diaphragms in a common diaphragm plane corresponding largely to the parting plane, being arranged vertically one above the other and being clamped between the outlet housing and the inlet housing. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged radially adjacent to one another in the inlet housing, with their respective actuation axes aligned horizontally and opposite switching directions, approximately centrally and at right angles to the compressed air inlets and compressed air outlets and parallel to the parting plane. The solenoids of the pilot valves are arranged in a magnet block, which is arranged, together with the mechanical components used in the solenoid valves, between a housing top part and a housing bottom part of the inlet housing. To ensure sealing, seals or sealing rings are arranged between the magnet block, the valve blocks and the valve seats of the solenoid valves, on the one hand, and the housing top part and housing bottom part of the inlet housing, on the other hand. To fix the housing top part and the housing bottom part to the magnet block of the solenoid valves, on the one hand, and to clamp the diaphragms of the diaphragm valves, on the other hand, the housing top part and the housing bottom part of the inlet housing are each screwed to the outlet housing. Thus, the valve unit comprises a very large number of components, which are relatively difficult to assemble. The production and assembly of this known valve unit is therefore relatively complicated and expensive.
Finally, DE 10 2008 028 439 B3 describes a valve unit of this kind in which an elongate valve housing is subdivided into a housing bottom part, a housing top part and an intermediate plate arranged therebetween, with parting planes that are largely horizontal in the installed position. The brake pressure inlet, the brake pressure outlet, and the vent outlet are each arranged in horizontal alignment in the housing bottom part. The diaphragm valves are arranged in series in the longitudinal direction in the housing bottom part, with parallel actuation axes and arrangement of the diaphragms in a common diaphragm plane corresponding to a large extent to the parting plane between the housing bottom part and the intermediate plate, being clamped between the housing bottom part and the intermediate plate. The pilot valve of the inlet valve and the pilot valve of the outlet valve are arranged radially adjacent to one another, approximately centrally above the diaphragm valves, in the housing top part, with their respective actuation axes aligned vertically and with the same switching directions, with the result that the overall height of the housing top part and hence of the valve unit as a whole is relatively large. The intermediate plate is screwed to the housing bottom part. The housing top part is screwed to the intermediate plate or the housing bottom part via an outer cover. Seals are arranged in the parting plane between the housing top part and the intermediate plate. This valve unit too thus comprises a very large number of components, although they can be assembled in a relatively simple manner from above. However, the production and assembly of this known valve unit are regarded as relatively expensive.